Fix unnecessary break when calculating the height of visible lines

[Rindbee]

This break causes the minsize to be smaller than expected, and then the size keeps increasing by one line to cover all visible lines. This can cause performance issues when there are many visible lines.

Fix #77268.

[Calinou]

Tested locally (rebased against master a83eb16), it works.

With a debug editor build (optimize=none):

• master: It takes 18.99 seconds for time godot --path ~/Downloads/Godot4LargeLabel/ --quit to run.
• This PR: It takes 1.54 seconds for time godot --path ~/Downloads/Godot4LargeLabel/ --quit to run.

[akien-mga]

CC @bruvzg

[akien-mga]

Thanks!

[akien-mga]

Note for @YuriSizov: If we want to cherry-pick this for 4.1.x (which may be good given that it fixes a significant performance issue), we need to handle #80218 there too. Your diff in #80218 (comment) might be suitable?

[YuriSizov]

@akien-mga Unfortunately that diff can only be used as a reference. In 4.1 we would need to give min sizes to labels in each validation form individually. The principle would be the same, just a bit more laborious.

[YuriSizov]

Given that we can trace various sizing issues to this PR, I wouldn't go for cherry-picking it into 4.1. If we were to do this, we would need to port all follow-up fixes as well, which seems more effort than it's worth at this point.